Magnetic memories, particularly magnetic random access memories (MRAMs), have drawn increasing interest due to their potential for high read/write speed, excellent endurance, non-volatility and low power consumption during operation. An MRAM can store information utilizing magnetic materials as an information recording medium. One type of MRAM is a spin transfer torque random access memory (STT-RAM). STT-RAM utilizes magnetic junctions written at least in part by a current driven through the magnetic junction. A spin polarized current driven through the magnetic junction exerts a spin torque on the magnetic moments in the magnetic junction. As a result, layer(s) having magnetic moments that are responsive to the spin torque may be switched to a desired state.
For example, FIG. 1 depicts a conventional magnetic tunneling junction (MTJ) 10 that may be used in a conventional STT-RAM and that uses precessional switching. The conventional MTJ 10 typically uses conventional seed layer(s) 12 and includes a conventional antiferromagnetic (AFM) layer 14, a conventional pinned layer 16, a conventional tunneling barrier layer 18, a conventional free layer 20, a second conventional tunneling barrier layer 22, and a conventional pinned layer 24.
The conventional seed layer(s) 12 are typically utilized to aid in the growth of subsequent layers, such as the AFM layer 14, having a desired crystal structure. The conventional tunneling barrier layers 18 and 22 are nonmagnetic and are, for example, a thin insulator such as MgO.
The conventional pinned layers 16 and 24 and the conventional free layer 20 are magnetic. The magnetization 17 of the conventional pinned layer 16 is fixed, or pinned, in a particular direction, typically by an exchange-bias interaction with the AFM layer 14. The conventional free layer 20 has a changeable magnetization represented by easy axis 21. The magnetizations of the conventional pinned layer 16 and the conventional free layer 20 are thus oriented in plane. However, the conventional pinned layer 24 has its magnetization 25 oriented perpendicular to the plane of the layers.
The conventional MTJ 10 uses precession to switch the magnetization 21 of the conventional free layer 20. When a sufficient current is driven in the z-direction (along the positive or negative z-axis), a spin torque pulls the magnetization 21 of the conventional free layer 20 further from the easy axis 21. Because the free layer magnetization 21 is not along the easy axis, the demagnetization field of the free layer 20 is nonzero. The free layer magnetization precesses around this nonzero demagnetization field of the free layer 20. The free layer 20 may then switch from parallel to antiparallel to the magnetization 17 of the conventional pinned layer 16 or vice versa.
Although the conventional MTJ 10 may be written using spin transfer and used in an STT-RAM, there are drawbacks. If the current driven through the conventional MTJ 10 is not removed at a specific time, the magnetization of the conventional free layer 10 may precess back to its original position. Stated differently, the conventional free layer 20 may not switch if the timing of the removal of the current is not carefully controlled. The current may be removed and a current in the opposite direction may be used instead of a single current. However, the timing and shape of pulses may need to be closely controlled for such switching. Such close control of the current is generally undesirable. Alternatively, an external magnetic field may be applied to improve the switching reliability. However, in such conventional MTJs 10, the required external magnetic field increases as the size of the conventional MTJ decreases. Thus such a solution exhibits poor scalability. Thus, significant drawbacks exist to precessional switching in conventional MTJs 10.
Accordingly, what is needed is a method and system that may improve the precessional switching. The method and system described herein address such a need.